Cephalexin Dosing for Impetigo
For impetigo, cephalexin should be dosed at 250 mg four times daily (QID) in adults and 25-50 mg/kg/day divided into 3-4 doses in children. 1
Adult Dosing
The IDSA 2014 guidelines explicitly recommend cephalexin 250 mg QID orally for impetigo caused by Staphylococcus and Streptococcus 1. The FDA label confirms that the usual adult dose is 250 mg every 6 hours, with 500 mg every 12 hours reserved for specific infections like streptococcal pharyngitis and uncomplicated skin infections 2.
For impetigo specifically, stick with the 250 mg QID regimen as this is the guideline-recommended dose for this particular infection 1.
Pediatric Dosing
Children should receive 25-50 mg/kg/day divided into 3-4 doses 1, 2. The IDSA guidelines and FDA label are aligned on this dosing range.
Practical Pediatric Dosing by Weight:
- 10 kg (22 lb): 1/2 to 1 teaspoon of 125 mg/5 mL suspension QID
- 20 kg (44 lb): 1 to 2 teaspoons of 125 mg/5 mL suspension QID
- 40 kg (88 lb): 2 to 4 teaspoons of 125 mg/5 mL suspension QID 2
Alternatively, for streptococcal pharyngitis and skin infections, the total daily dose may be divided and given every 12 hours (BID) 2.
Treatment Duration
Continue therapy for at least 10 days when treating β-hemolytic streptococcal infections 2. For impetigo, a standard 10-day course is appropriate 3.
Clinical Evidence Supporting Cephalexin
Research demonstrates cephalexin's superiority over penicillin V for impetigo, with treatment failure rates of 0% for cephalexin versus 24% for penicillin V 3. This is because Staphylococcus aureus (the predominant pathogen in 62-81% of impetigo cases) is often penicillin-resistant but remains susceptible to cephalexin 3, 4.
Important Caveats
MRSA consideration: While guidelines recommend cephalexin for typical impetigo, if MRSA is suspected or confirmed (patient with recurrent infections, failed initial therapy, or known MRSA colonization), switch to an MRSA-active agent like clindamycin 300-400 mg QID in adults or 20 mg/kg/day in 3 divided doses in children 1
Topical alternatives: For patients with limited lesions, mupirocin or retapamulin ointment applied twice daily may be sufficient 1
Dosing frequency: While some studies show BID dosing may be effective for certain skin infections 5, 6, the guideline-recommended QID dosing should be used for impetigo to ensure adequate coverage 1